1. Field of the Invention
The present invention relates to an image display apparatus and is suitable for use in, for example, a head mounted image display apparatus.
2. Related Background Art
In recent years, mixed reality (MR) techniques have been known as techniques for seamlessly merging the real world with the virtual world in real time, that is, techniques capable of integrating the real world with the virtual world in real time with comfortable feeling to use the integrated world.
The following technique has been proposed as one of the MR techniques. According to this technique, a video see-through HMD (head mounted display) is used. An image of a subject substantially identical to a subject observed at an eye position of a person on whom the HMD is mounted is picked up by a video camera or the like. The picked up image is overlapped with computer graphics (CG) to display an overlapped image such that the person on whom the HMD is mounted can observe the overlapped image.
FIG. 6 is a structural view showing a conventional video see-through HMD. Because of a pair of structures for right and left eyes, a structure for only one of the eyes is shown in FIG. 6. The HMD includes a display device 201 composed of a small-size liquid crystal display for right eye or left eye and the like, a display optical system 202 such as a free-form curved surface prism for enlarging an image for right eye or left eye, which is displayed on the liquid crystal display, an image pickup device 301 for picking up an image of a subject substantially identical to an object (subject) observed at a position of an eye 401 of a person on whom the HMD is mounted, and an image pickup optical system 302 for substantially aligning the eye 401 of the person on whom the HMD is mounted with the image pickup device 301.
FIG. 7 is an external view showing a video see-through HMD 501 which is mounted on a person. FIG. 8 is a simple block diagram of the video see-through HMD 501. The video see-through HMD 501 includes image pickup units 510R and 510L for picking up images to be displayed in the HMD 501, an image processing unit 540 for performing image processing such as CG overlapping on the picked up images, and display units 520R and 520L for displaying composite images in which the picked up images are combined with the CG.
The image pickup unit 510R (510L) includes an image pickup device 511R (511L) such as a CCD image sensor or a CMOS image sensor, an AD conversion portion 512R (512L) for performing processings such as gain adjustment and correlated double sampling (CDS) on an analog signal outputted from the image pickup device 511R (511L) and then converting the processed analog signal into a digital signal, a digital signal processing portion 513R (513L) for performing processings such as gain control, color tint control, brightness control, and gamma correction on the digital signal, and a picked-up-image outputting portion 514R (514L) for outputting a picked-up-image signal to an outside.
The image processing unit 540 is composed of a personal computer, a workstation, or the like. The display unit 520R (520L) includes a display device 521R (521L) using polysilicon (p-Si) TFTs, liquid-crystal-on-silicon (LCOS), or the like, a display drive portion 522R (522L) for controlling and driving the display device 521R (521L), and a display image inputting portion 523R (523L) for receiving a display image signal inputted from an outside.
When the video see-through HMD having the above-mentioned structure is mounted on a person, the person can experience a mixed reality world in which the real world is seamlessly merged with the virtual world in real time (see Japanese Patent Application Laid-Open No. 2001-133725 (paragraphs 0026 to 0036 and FIG. 1) (corresponding to EP 1098217 A1)).
However, when a malfunction such as false operation or failure in an image pickup unit which is composed of a video camera and the like occurs in the conventional video see-through HMD, there is the following problem. That is, in such a case, an image is not outputted from the image pickup unit in which the malfunction occurs to display no image on a corresponding display unit, or an image in which noises and the like are generated is displayed on the display unit.
Warning or displaying corresponding to the malfunction of the image pickup unit is not performed. Of a plurality of image pickup units provided in the video see-through HMD, an image pickup unit in which the malfunction occurs cannot be determined. A trouble portion of the image pickup unit in which the malfunction occurs cannot also be determined. Therefore, it is impossible to smoothly deal with the malfunction up to now.